This is a study of wound healing: Why do wounds begin to heal? Why do they cease healing? What is the significance of the impaired (injured) blood supply which characterizes wounds? How does oxygen supply affect repair and resistance to infection? Why do adrenocorticosteroids suppress repair and resistance to infection and why does vitamin A reverse this effect? What is the vitamin A requirement for massively injured (burned) patients? How can one diagnose and correct the causes of inadequate repair in patients? Why do patients with diseases of connective tissue heal poorly and what can be done about it? Why does diabetes profoundly affect healing? The answers lie in few cell types, the fibroblast, the macrophage, the granulocyte and the capillary endothelial cell. The studies are all interrelated, and the proposals closely interact. Through them, we have recently come very close to disclosing the mechanism of how healing starts and stops.